Papertrail can create and update a metric on HostedGraphite with the number of log messages matching a search alert, which can then be visualized within the HostedGraphite app.
Follow the steps in Alerts.
In HostedGraphite, the metric name will appear with the sender name appended to it, so that counts can be analyzed per-sender.
Because Papertrail is sending a count of events (Counter metric), use the
sumdata view to see an accurate visualization in Grafana graphs.